Pernosco accepts uploaded rr recordings from customers and replays them with binary instrumentation to build a database of all program execution, to power an amazing debugging experience. Our infrastructure is Intel-based AWS instances. Some customers upload recordings made on AMD (Zen) machines; for these recordings to replay correctly on Intel machines, instruction execution needs to produce bit-identical results. This is almost always true, but I recently discovered that the approximate arithmetic instructions RSQRTSS, RCPSS and friends do not produce identical results on Zen vs Intel. Fortunately, since Pernosco replays with binary instrumentation, we can insert code to emulate the AMD behavior of these instructions. I just needed to figure out a good way to implement that emulation.

source: HN

Kyle convinced me that trace stability and portability were worth a major version bump.

source: L

I recently discovered the obscure XGETBV instruction.

source: L

To be clear: I don’t want to work on this. I’m a lot more interested in the applications of record-and-replay than the machinery that does it. I want someone else to do it for us

I may never tire of printf debugging, but if some day I do, I will try rr.

source: L